¶3Upon review, we conclude that "motor vehicle fuel"
does not include aviation fuel, that the minimum markup provisions in Chapter
100 of the Wisconsin Statutes do not apply to aviation fuel, and that Orion
cannot rely on Wis. Stat. § 100.30 for a private cause of action
against Basler.We also conclude that
the Wisconsin Administrative Code § ATCP 105.001(4) (Sept., 1990) does not
incorporate aviation fuel in its definition of "motor vehicle fuel,"
and is thus consistent with the statute.We therefore affirm the court of appeals' decision reversing the circuit
court's preliminary injunction.

I

¶4The relevant facts are undisputed.In 1957, Winnebago County and Basler entered into an agreement
for Basler to sell aviation fuel at the Wittman Regional Airport
("Wittman") in Oshkosh, Wisconsin.Basler is a Fixed Based Operation ("FBO"), which is a vendor
of services at an airport or airfield.Basler sells "Jet A fuel" and "100 LL aviation fuel"
at Wittman through a self-service pump for use by airplane owners, as well as
through the use of a fleet of trucks that deliver the fuel to aircrafts.Basler continues to operate under this
agreement.

¶5From 1957 to 2002, Basler had been the sole provider of aviation
fuel for Wittman, and the only FBO under an agreement with Winnebago
County.However, on May 29, 2002,
Winnebago County entered into an agreement with Orion to sell aviation fuel at
Wittman.Orion, like Basler, sells Jet
A fuel and 100 LL aviation fuel.Unlike
Basler, Orion only delivers the fuel to aircrafts and does not operate
self-service pumps.

¶6 In 2002 and early 2003, the parties engaged in a "price
war" where the price of aviation fuel at Wittman dropped from $2.59 to a
low of $1.599 per gallon.[4]In November 2002, Orion filed a complaint
with the Wisconsin Department of Agriculture, Trade and Consumer Protection
("DATCP").Orion alleged that
when Basler set its price of fuel at $1.599 per gallon, Basler set its fuel
price below cost, in violation of the Unfair Sales Act,
Wis. Stat. § 100.30(3).[5]DATCP began an investigation into Basler's
fuel prices.[6]

¶7On March 19, 2003, before DATCP completed its investigation,
Orion filed a suit in Winnebago County alleging that Basler sold motor vehicle
fuel below the statutory minimum required for motor vehicle fuel, in violation
of the Unfair Sales Act, and seeking injunctive relief.

¶8Two days after Orion filed this suit, Basler received a warning
letter from DATCP.DATCP concluded that
Basler's "cost" of the 100 LL aviation fuel was $1.78, and therefore
Basler violated Wis. Stat. § 100.30 when it sold its 100 LL
aviation fuel at prices below $1.78.[7]In the warning letter, DATCP further
concluded that the minimum markup requirement under the Unfair Sales Act for
sales of "motor vehicle fuel" did not include aviation fuel.

[W]e have explored the issue of whether or not 100 LL
aviation fuel should be treated as "motor vehicle fuel" under the
Unfair Sales Act . . . .We have concluded that 100 LL aviation fuel is not "motor vehicle
fuel" as the term is used in the statute.We base this conclusion on the common sense fact that airplanes are
generally not considered "motor vehicles" under various transportation
statutes and codes.Furthermore, it
seems illogical that the term "motor vehicle fuel" as it is used in
the statute was intended to be used outside of the contents of sales of fuel
intended for highway use through the well established industry of retail gas
stations and convenience stores.[8]

¶9Although DATCP concluded that aviation fuel was not "motor
vehicle fuel," it also warned Basler that "any person who is injured
as a result of a competitor selling motor vehicle fuel below cost may
sue for $2,000 per day or treble actual damages, whichever is greater, plus
reasonable accounting and attorney fees."[9]In addition, later that same day, DATCP
followed up with a second letter to Basler, stating that

[S]ome additional information has come to our attention
regarding the question of whether aviation fuel is covered under the Unfair
Sales Act as "motor vehicle fuel."Based on this new development, we have decided that we need to do
additional research on this question before we issue a final interpretation on
this issue.Specifically, in the first
paragraph on page 2 of the warning letter, we state an opinion that 100 LL
aviation fuel is not "motor vehicle fuel" under the Unfair Sales
Act.That paragraph and the opinion
it expresses is hereby retracted.However, the remainder of the warning letter still stands.[10]

¶10This second letter explicitly retracts "the opinion that
100 LL aviation fuel is not 'motor vehicle fuel.'"However, DATCP failed to retract its
conclusion that the cost for Basler's 100 LL aviation fuel was $1.78.The analysis used to reach the $1.78 figure
did not include a minimum markup calculation.[11]See Wis. Stat. § 100.30(2)(am)1m.a. to e.Moreover, the record contains no final
interpretation of "motor vehicle fuel," and no final order from
DATCP.

The definition is clear to me and under the
circumstances as we have them here the fuel that is being used is being placed
into what I would consider to be under that definition a motor vehicle for
purposes of the Unfair Sales Act.

¶13The circuit court ordered Basler to "immediately refrain
from selling 100 LL fuel 'below cost' as defined in
Wis. Stat. § 100.30(2)(am)1m.c."[13]The circuit court based its decision on the
definition of motor vehicle fuel in Wis. Admin. Code § ATCP 105.001(4).[14]The court reasoned that the definition of
motor vehicle is unambiguous in the code, and under the circumstances of the
facts of this case, the fuel sold by Basler and Orion constitutes "motor
vehicle fuel" for purposes of the Unfair Sales Act.

¶14Basler filed an interlocutory appeal. The court of appeals
granted leave to appeal and reversed. The court of appeals concluded that
including aviation fuel in the definition of "motor vehicle fuel"
strayed too far from the legislature's intent.[15]The court of appeals also concluded that
because the Unfair Sales Act excludes aviation fuel from the definition of
"motor vehicle fuel," "the DATCP's definition may extend no
further."[16]

¶15Orion asks this court to reverse the court of appeals and find
that "motor vehicle fuel" includes aviation fuel for purposes of the
Unfair Sales Act.Orion contends that
the court of appeals unnecessarily limited the definition of "motor
vehicle fuel."In contrast, Basler
asks this court to affirm the court of appeals, asserting that the language of
the statute, along with its context, structure, and its relationship with other
statutes, indicate that aviation fuel is not "motor vehicle fuel"
within the meaning of the Unfair Sales Act.

II

¶16This case presents a question of statutory interpretation, which
we review de novo. State v. Reed, 2005 WI 53, ¶13, 280
Wis. 2d 68, 695 N.W.2d 315.The purpose of statutory interpretation is to determine what a statute
means in order to give the statute its full, proper, and intended effect.Id."We begin with the statute's language because we assume that the
legislature's intent is expressed in the words it used."Id.Generally, language is given its common, ordinary, and accepted
meaning.Kalal v. Dane County Cir.
Ct., 2004 WI 58, ¶45, 271 Wis. 2d 633, 681 N.W.2d 110.In addition, statutory language is
interpreted in the context in which it is used, in relation to the language of
surrounding or closely-related statutes, and interpreted to avoid absurd or
unreasonable results.Id.,
¶46.

¶17"If the meaning is plain, we ordinarily stop the
inquiry."Reed, 280
Wis. 2d 68, ¶13.However, if
a statute is ambiguous, we examine extrinsic sources, such as legislative
history, to ascertain the legislative intent.Kalal, 271 Wis. 2d 633, ¶48.A statute is ambiguous if "[t]he statute's ability to
support two reasonable constructions creates an ambiguity which cannot be
resolved through the language of the statute itself.[A] statutory provision is ambiguous if reasonable minds could
differ as to its meaning."UFE
Inc. v. LIRC, 201 Wis. 2d 274, 283, 548 N.W.2d 57 (1996) (quotation
omitted).

¶19We begin our analysis of whether the Unfair Sales Act applies to
aviation fuel with an examination of the statute.

¶20The Unfair Sales Act establishes a statutory scheme for
regulating vendor pricing in Wisconsin.Although the Unfair Sales Act prohibits all vendors from selling
merchandise below cost,[18]
the Act establishes a particular pricing scheme for "motor vehicle
fuel" by defining "cost" for the sale of "motor vehicle
fuel" to include a markup, ranging from 3 percent to 9.18 percent.[19]This minimum legal selling price is referred
to as a "minimum markup."The
statute also contains markup provisions for computing costs for
"cigarettes or other tobacco products, fermented malt beverages or intoxicating
liquor or wine."[20]No other merchandise is currently subject to
a minimum markup.[21]

¶21Under the Unfair Sales Act:

Any sale of any item of merchandise either by a
retailer, wholesaler, wholesaler of motor vehicle fuel or refiner, at less than
cost as defined in this section with the intent or effect of inducing the
purchase of other merchandise or of unfairly diverting trade from a competitor,
impairs and prevents fair competition, injures public welfare and is unfair
competition and contrary to public policy and the policy of this section.Such sales are prohibited. Evidence of any
sale of any item of merchandise by any retailer, wholesaler, wholesaler of
motor vehicle fuel or refiner at less than cost as defined in this section
shall be prima facie evidence of intent or effect to induce the purchase of
other merchandise, or to unfairly divert trade from a competitor, or to
otherwise injure a competitor.[22]

¶22The statute also establishes a private right of action for
merchants who sell motor vehicle fuel below cost, as defined in subsection
(3).Wis. Stat. § 100.30(5m).Under this subsection, "Any person who is injured or threatened
with injury as a result of a sale or purchase of motor vehicle fuel" is
authorized to bring an action against the merchant who violated this statute
for "temporary or permanent injunctive relief" or for treble damages
or $2,000 for each day the violation continues, whichever is greater.Id.[23]

¶23The question before this court is whether the legislature
intended aviation fuel to constitute "motor vehicle fuel" under the
Unfair Sales Act.

¶25Orion asserts that the meaning of "motor vehicle fuel"
clearly and unambiguously includes aviation fuel, and therefore the court need
not examine any extrinsic materials to discern the legislature's intent.Orion contends that dictionary definitions
of the words "motor," "vehicle," and "fuel," when
considered together, compel the conclusion that the term "motor vehicle
fuel" means a combustible matter used to run a comparatively small and
powerful engine, such as an internal combustion engine, in any means of
conveyance, which would include an aircraft.Basler counters that a phrase must be understood according to its common
usage and cannot be parsed into its least common denominators and recast into
something new.Basler implies that
Orion's method produces absurd results, suggesting that, under Orion's
approach, a "hot dog" would be defined as a domesticated, carnivorous
animal that radiates heat.Basler
offers its own definition, contending that the plain meaning of "motor
vehicle" commonly refers to fuel used by cars, trucks, and similar
earth-bound vehicles.

¶26We find no dictionary definition for the phrase "motor
vehicle fuel."The
dictionary defines "motor vehicle" as "[a] self-propelled
wheeled conveyance, such as a car or truck, that does not run on
rails."American Heritage
Dictionary of English Language, 1179 (3d ed. 1992).In addition, though we find no definition of
"aviation fuel," the dictionary defines "airplane" as
"various winged vehicles capable of flight, generally heavier than air and
driven by jet engines or propellers."Id. at 39.Neither of
these definitions, nor the definitions proffered by the parties, clarify
whether motor vehicle fuel includes aviation fuel.We therefore consider other intrinsic sources, such as the
statement of purpose and the context in which statutory language is used.Kalal, 271 Wis. 2d 633,
¶49.We begin by examining the
legislature's statement of legislative intent.

B

¶27The Wisconsin Legislature included a statement of policy when it
passed the Unfair Sales Act.The policy
states:

The practice of selling certain items of merchandise
below cost in order to attract patronage is generally a form of deceptive
advertising and an unfair method of competition in commerce. Such practice
causes commercial dislocations, misleads the consumer, works back against the
farmer, directly burdens and obstructs commerce, and diverts business from
dealers who maintain a fair price policy.Bankruptcies among merchants who fail because of the competition of
those who use such methods result in unemployment, disruption of leases, and
nonpayment of taxes and loans, and contribute to an inevitable train of
undesirable consequences, including economic depression.

¶28Under this express statement of intent, the policy of
Wis. Stat. § 100.30 is to protect Wisconsin consumers and
merchants against unfair competition in commerce.The statute seeks to achieve this policy by prohibiting the sale
of merchandise below cost.[25]This court has previously recognized that
the legislative intent behind other state statutes similar to the Unfair Sales
Act is to address an "economic evil"[26]
and "promote[] the general welfare" by fostering free, open, and fair
competition.[27]

¶29In concluding that "motor vehicle fuel" does not
include aviation fuel for purposes of the Unfair Sales Act, the court of
appeals relied heavily on its determination that "the legislature intended
the Unfair Sales Act to prevent large vendors from driving small
competitors out of business . . ." and that common sense
would clearly reveal that the aviation fuel market is outside the scope
"of the 'mom and pop' businesses the legislature intended to
protect."Orion, 277
Wis. 2d 819, ¶¶22-23 (citation omitted).

¶30Orion contends that the court of appeals improperly concluded
that the legislative intent behind the Unfair Sales Act did not include FBOs
because they are not "mom and pop" businesses.Basler's pricing scheme, Orion asserts, is
exactly the type of unfair competition the legislature intended to ban through
the Unfair Sales Act in an attempt to protect consumers and businesses.Orion asks this court to conclude that the
Unfair Sales Act applies to more than "mom and pop" convenience
stores.

¶31Upon review we find nothing in the stated purpose of legislative
intent that limits the Unfair Sales Act to "mom and pop"
establishments.The purpose of the Act
is to protect consumers against unfair pricing.To that effect, it is not disputed that Basler is prohibited
under the Act from selling its fuel below cost.But that is not the question before this court.We must determine whether the cost of aviation
fuel is to be calculated as "motor vehicle fuel" and therefore
subject to the minimum markup, or whether the cost of aviation fuel is to be
calculated like all other merchandise.There is nothing in the stated purpose, or in the public policy
recognized by this court in other cases, that suggests whether selling aviation
fuel with or without the minimum markup would constitute a greater economic
evil, foster unfair competition, or harm Wisconsin consumers.

¶33Orion contends that the circuit court properly determined that
Chapter 78 and Wis. Stat. § 100.30 are not "related"
because they concern different areas of law; Chapter 78 is a taxation statute,
whereas Chapter 100 addresses trade and marketing.Therefore, according to Orion, the definition of "motor
vehicle fuel" in Chapter 78 is inapplicable to § 100.30.

¶34In contrast, Basler urges
this court to conclude that the Unfair Sales Act must be read together with
Chapter 78, which defines and distinguishes "motor vehicle fuel" and
"aviation fuel," because the statutes relate to the same subject
matter: Chapter 78 establishes the state excise taxes that a fuel seller must
use to determine its minimum sale price for motor vehicles under the Unfair
Sales Act.According to Basler,
interpreting the term "motor vehicle fuel" in
Wis. Stat. § 100.30 to include aviation fuel would result in an
absurd contradiction: the same aviation fuel would be subject to "aviation
fuel" calculations under one statute (Chapter 78), but subject to
"motor vehicle fuel" calculations under a related statute (Chapter
100).This would create a conflict and
an absurd relationship between the Unfair Sales Act and Chapter 78.

¶35We find Basler's argument persuasive.Chapters 78 and 100 relate to the same subject matter.This court should therefore attempt to
harmonize the two chapters, if possible, to avoid absurd results.State v. Wachsmuth, 73
Wis. 2d 318, 326-30, 243 N.W.2d 410 (1976) (concluding that when
two statutes are "inparimaterial, the court must
harmonize them if possible").

"General aviation fuel" means products placed
in the fuel supply tank of aircraft, commonly or commercially known as
aviation gasoline and jet turbine fuel and other combustible gases and
liquids suitable for the generation of power for propulsion of aircraft.[28]

¶38It is clear from the Chapter 78 definitions that with respect to
Chapter 78, the legislature has defined "motor vehicle fuel" as
gasoline or diesel fuel used in vehicles capable of being driven on a highway,
while general aviation fuel is defined as that which is specifically designed
for aircraft.The legislature
approached these fuels differently for purposes of Chapter 78.

¶39In addition to Chapter 78, Orion also asserts that the court of
appeals improperly relied on the definition of the term "motor
vehicle" in Wis. Stat. § 340.Although other sections of Chapter 100 cross-reference Chapter 340,
the Unfair Sales Act does not.Basler
counters that although the term "motor vehicle" is not defined in
Wis. Stat. § 100.30, numerous sections of Chapter 100 reference
the definition of vehicle in chapter 340, which, like Chapter 78, limits the
definition to highway use.

¶40Upon review, we find five subsections of Chapter 100 that
currently cross-reference the term "motor vehicle" as defined in
Wis. Stat. § 340.01(35).[29]Chapter 340 refers to vehicles that are used
on land and does not include airplanes.[30]

¶41Examining Wis. Stat. § 100.30 in the context of
Chapter 78, as well as in the context of the cross-references between Chapter
100 and § 340.01(35), we determine that when the legislature has defined
"motor vehicle" or "vehicle," it has continuously
referenced conveyances that operate on land and has not included aircraft.

¶42However, these statutory definitions of "motor
vehicle," "motor vehicle fuel" and "general aviation
fuel" are not cross-referenced in Wis. Stat. § 100.30.When a statute with respect to one subject
contains a given provision, "the omission of such provision from a similar
statute concerning a related subject is significant in showing that a different
intention existed."Kimberly-Clark
Corp. v. Pub. Serv. Comm'n of Wisconsin, 110 Wis. 2d 455, 463,
329 N.W.2d 143 (1983) (quoting State v. Welkos, 14
Wis. 2d 186, 192, 109 N.W.2d 889 (1961)).[31]

¶43We cannot ignore the legislature's consistent definitions of
"motor vehicle" and "motor vehicle fuel" throughout the
Wisconsin Statutes, nor can we ignore the fact that
Wis. Stat. § 100.30 does not explicitly cross-reference any of
these statutory definitions of "motor vehicle" or "motor vehicle
fuel."We therefore conclude that the
language of the surrounding and closely-related statutes fails to clarify the
meaning of "motor vehicle fuel" in § 100.30 as to whether it
includes "aviation fuel."

D

¶44Orion asserts that the plain language of this statutory
definition of "motor vehicle fuel" includes gasoline used to power
numerous types of motor vehicles, including aircraft, boats, farm equipment,
construction machinery, motorcycles, and snowmobiles.In contrast, Basler contends that "motor vehicle fuel"
refers to the fuel used by cars, trucks, and similarly earthbound vehicles, and
therefore the statutory language clearly does not include aviation fuel.

¶45Simply because parties disagree on the "plain"
interpretation of a statute does not make the statute ambiguous.Preston v. Meriter Hosp., Inc., 2005
WI 122, ¶20, 284Wis. 2d 264,
700 N.W.2d 158.However, we agree with
the court of appeals and find that "neither party advances a definition
wildly at odds with common sense."Orion, 277 Wis. 2d 819, ¶21.In addition, neither party advances a definition at odds with the
plain meaning of the statute.The use
of the term "motor vehicle fuel" in
Wis. Stat. § 100.30, therefore, supports two reasonable
constructions that cannot be resolved through the language itself.SeeUFE, 201
Wis. 2d at 283.We conclude
that the statute is ambiguous because it is open to more than one reasonable
interpretation.We therefore turn to
extrinsic sources to determine the legislative intent.

IV

¶46Because we find the Unfair Sales Act ambiguous, we review the
relevant administrative code provision, DATCP's interpretations of the statute
and code, and the legislative history of the statute.SeeKalal, 271 Wis. 2d 633, ¶¶48, 50; UFE,
201 Wis. 2d at 282-83.

A

¶47We begin with an examination of the administrative code
provision that defines "motor vehicle fuel" for purposes of the
Unfair Sales Act.The Wisconsin
Statutes authorize the legislature to delegate the authority to administrative
agencies to make rules necessary to effectuate a statute.Wis. Stat. § 227.11(2)(a).When an agency issues a rule pursuant to its rule-making
authority, that rule has the effect of law.Wis. Stat. § 227.01(13).Our analysis reveals that the administrative code is ambiguous.

¶48The Wisconsin Legislature granted DATCP the authority to
promulgate regulations to implement Chapter 93 through Chapter 100 of the
Wisconsin Statutes.[32]Pursuant to this rule-making authority,
DATCP issued a rule that defined "motor vehicle fuel" in the
Wisconsin Administrative Code as follows:

"Motor vehicle fuel" means any liquid
prepared, advertised or sold for use as or commonly and commercially used as
fuel in internal combustion engines.

Wis. Admin. Code § ATCP
105.001(4).

¶49Orion asserts that DATCP properly promulgated a definition of
"motor vehicle fuel" that indicates that aviation fuel constitutes
motor vehicle fuel, and that the definition is entirely consistent with the
purposes of the Unfair Sales Act.[33]According to Orion, the only limitation on
motor vehicle fuel under ATCP § 105.001(4) is that the fuel must be used
in an internal combustion engine, and this limitation does not exclude aviation
fuel.Orion contends that the court of
appeals ignored the clear and unambiguous definition of motor vehicle fuel in
§ ATCP 105.001(4).Orion further
contends that Basler was required to first file a separate declaratory judgment
action to invalidate the rule under Wis. Stat. § 227.40.[34]

¶50In contrast, Basler contends that the court of appeals correctly
rejected Orion's argument that the DATCP regulation should be read expansively
to include aviation fuel.According to
Basler, the history of the regulation demonstrates that DATCP used Chapter 78
to create the definition, intending to limit "motor vehicle fuel" to
fuel used by conveyances that are "self-propelled by an internal
combustion engine or motor and licensed for highway
use . . . ."Wis. Stat. § 78.03(1) (1990).In addition, Basler asserts that the history of the rule is consistent
with DATCP's interpretations in its warning letter to Basler.In response to Orion's assertion that the
court lacks competence to proceed because Basler failed to file a declaratory
judgment action under Wis. Stat. § 227.40, Basler contends that
this statute only applies when a party seeks to invalidate a rule and Basler is
not seeking to invalidate a rule.

¶51Because administrative code provisions are subject to rules of
statutory construction, Basinas, 104 Wis. 2d at 546, we do not
reach the history of § ATCP 105.001, on which Basler relies, unless we
find the rule ambiguous.Under
§ ATCP 105.001(4), "motor vehicle fuel" includes "any
liquid" that is used in an "internal combustion engine."The definition is silent with regard to
general aviation fuel.Moreover, the
code provision makes no reference to aviation gasoline or jet turbine fuel.The code provision, therefore, fails to
clarify the same term used in the statute that we concluded was susceptible to
more than one reasonable interpretation with regard to aviation fuel.Like a statute, "[a] rule is ambiguous
if reasonable persons can understand it differently."Staples, 142 Wis. 2d at
354.We conclude that the code
provision is ambiguous as to whether "motor vehicle fuel" includes
aviation fuel.We therefore turn to the
history of the formation of Wis. Admin. Code § ATCP 105.001(4) and the
agency's interpretations of the regulation to determine the agency's intent and
resolve the ambiguity in § ATCP 105.001(4).

1

¶52An analysis of the history of Wis. Admin. Code § ATCP
105.001 reveals that DATCP intended to make the definition of "motor
vehicle fuel" consistent with Chapter 78, excluding aviation fuel from the
definition.

¶54On June 22, 1989, after completing its analysis, the Legislative
Council sent to DATCP a Clearinghouse Report on Rule 89-91.[36]In the Clearinghouse Report, the Legislative
Council wrote: "It is not clear why the term 'motor vehicle fuel' is used
instead of 'motor fuel' or why a separate definition of the term is created
instead of using the statutory definition of 'motor fuel' contained in s.
78.04, Stats."Clearinghouse
Report, Rule 89-91 Comments, June 22, 1989.

[T]hese phrases have different meanings and [] the
unfair sales act specifically refers to "motor vehicle fuel" [draft],
not "motor fuel"."Motor
fuel" is defined in s. 78.04, Stats., to cover only gasoline and some
naphthas.It excludes diesel and
other special fuels, while "motor vehicle fuel," according to the
definition of "motor vehicle" in s. 78.03(1) [89-90], Stats., includes
diesel and other special fuels.These
terms are not synonymous, and the distinction between them must be taken into
consideration . . . .

"Motor vehicle" means any automobile, truck,
truck-tractor, tractor, bus, vehicle or other conveyance that is self-propelled
by an internal combustion engine or motor and licensed for highway use,
except that "motor vehicle" does not include mobile machinery and
equipment.

Wis. Stat. § 78.005(12)
(emphasis added).

¶57The rule was referred to the committee on Commerce and Consumer
Affairs on March 12, 1990.The review
period ended without objection from the legislature,[40]
and DATCP promulgated the rule, unchanged, effective September 1, 1990.

¶58DATCP's March 5, 1990, letter to the legislature explaining its
definition of "motor vehicle fuel" reveals the agency's intent in
structuring its definition.The agency
clearly intended to define the term "motor vehicle fuel" to include
more than gasoline, but to limit the definition to ensure the administrative
rule was consistent with Wis. Stat. § 78.03(1) (1989-90).As a result, in implementing this rule,
DATCP limited the definition of "motor vehicle fuel" to gasoline,
diesel, and other special fuels used to power vehicles that are
"self-propelled by an internal combustion engine or motor and licensed for
highway use"[41]
as defined in Chapter 78.[42]This historical analysis clarifies that
DATCP did not intend for general aviation fuel to fall within its definition of
motor vehicle fuel.

2

¶59We next examine DATCP’s interpretation of the statute and the
applicable portions of the administrative code as contained in its preliminary
warning letters to Basler.We conclude
that DATCP's interpretations of the administrative code in this case offer no
guidance for our analysis.

¶60This court ordinarily gives deference to a state agency's
settled "interpretation and application of its own administrative
regulations unless the interpretation is inconsistent with the language of the
regulation or is clearly erroneous."Bergmann, 211 Wis. 2d at 7 (citations omitted).Because the record in this case reveals that
there is no settled agency interpretation, it is clear that the preliminary
warning letters at issue in this case should not be given any deference.We therefore examine the meaning of the
administrative code independently.SeeId. at 8.

¶61The record in this case indicates that there is no settled
department interpretation of the regulation at issue.DATCP issued a preliminary warning letter informing Basler that
"motor vehicle fuel" did not include aviation fuel, yet warned Basler
that "any person who is injured as a result of a competitor selling motor
vehicle fuel below cost may sue . . . ."[43]Moreover, hours after issuing this warning
letter to Basler, DATCP retracted its conclusion that "motor vehicle
fuel" did not include aviation fuel.[44]In this retraction, DATCP stated it needed
to conduct "additional research on this question before we issue a final
interpretation" with regard to aviation fuel.[45]The record does not contain any "final
interpretation" by DATCP.

¶62Whether Wisconsin courts should give deference to a preliminary
agency interpretation is irrelevant under the facts of this case, as no level
of deference would be applicable to the inconsistent warning letters that were
issued by DATCP. In its warning letters, DATCP's inconsistent interpretations
of "motor vehicle fuel" under § ATCP 105.001 offer no guidance
to this analysis.We draw no
conclusions as to whether, in general, an agency's interpretations of a statute
or an administrative code that is embodied in warning or opinion letters should
be given deference by this court.[46]Our examination of these letters simply
demonstrates the agency’s confusion in interpreting the statute.

B

¶63We have concluded that the definition of "motor vehicle
fuel," promulgated by DATCP in § ATCP 105.001(4) excludes aviation
fuel.The validity of this rule depends
upon whether the rule exceeds the bounds of Wis. Stat. § 100.30.We therefore examine the legislative history
of the statute in an effort to discern whether the rule is consistent with the
statute.We conclude that the
legislature intended to limit the application of the minimum markup provisions,
and that "motor vehicle fuel" should be read narrowly to exclude
aviation fuel.

¶64In 1939, the Wisconsin Legislature enacted the Wisconsin Unfair
Sales Act, Wis. Stat. § 100.30.[47]The 1939 Act established a minimum markup
price of 3 to 6 percent for all merchandise sold in Wisconsin.[48]The Act was amended several times but
remained relatively unchanged from its original form until 1986.[49]

¶65In 1986, the legislature significantly amended the Unfair Sales
Act.The original draft of 1985 Wis.
Act 313, Assembly Bill 219, would have eliminated the minimum markup for all
merchandise except for cigarettes sold by wholesalers and would have eliminated
the requirement that all other merchandise be sold at cost or higher.[50]Assembly Bill 219 was amended in order to
continue the markup for other tobacco products and motor vehicle fuel.[51]The bill was further amended to include
fermented malt beverages, intoxicating liquor, and wine.[52]The bill was also amended to continue to
prevent vendors from selling all merchandise below cost.[53]Amendments that would have continued the
minimum markup for "foreign owned companies"[54]
and "groceries"[55]
were rejected.The final revision to
the Unfair Sales Act eliminated the minimum markup provisions for all
merchandise except for "cigarettes or other tobacco products, fermented
malt beverages, intoxicating liquor or wine or motor vehicle fuel."[56]

¶66The legislative documents and news reports surrounding passage
of the bill indicate that the final law, 1985 Wis. Act 313, constituted a
compromise as to the particular merchandise that would retain the minimum
markup calculations in their definitions of "cost."[57]

¶67This history reveals that the legislature considered applying
the minimum markup to various products and carefully crafted the amendment to
limit the application of the minimum markup laws to particular
merchandise.

¶68In addition, as the court of appeals noted in this case, the
1986 amendment was the first time the term "motor vehicle fuel" was
used in the Unfair Sales Act.Orion,
277 Wis. 2d 819, ¶26.Yet,
when the legislature made this change, other provisions of Chapter 100
cross-referenced the term "motor vehicle" as defined in section 340:[58]

"Motor vehicle" means a vehicle which is
self-propelled, including a trackless trolley bus, except that a snowmobile
shall only be considered a motor vehicle for purposes made specifically
applicable by statute.[59]

Chapter 340 further defined
"vehicle":

"Vehicle" means every device in, upon or by
which any person or property is or may be transported or drawn upon a
highway, except railroad trains. A snowmobile shall not be considered a
vehicle except for purposes made specifically applicable by statute.[60]

¶69We conclude that the legislature intended the term "motor
vehicle fuel" to be read consistently with the terms "motor
vehicle" and "motor vehicle fuel" as defined and used in other
related statutes at the time the Unfair Sales Act was amended to include a minimum
markup for "motor vehicle fuel."The term "motor vehicle fuel" should be read narrowly to
evince this legislative intent.We
therefore conclude that the term "motor vehicle fuel" does not
include "aviation fuel."

V

¶70We conclude that "motor vehicle fuel" does not include
aviation fuel, that the minimum markup provisions in
Wis. Stat. § 100.30 do not apply to aviation fuel, and that
Orion cannot rely on § 100.30(5m) for a private cause of action against
Basler.We also conclude that
§ ATCP 105.001 is consistent with and does not exceed the bounds of
Wis. Stat. § 100.30.We
therefore affirm the court of appeals' decision.

[2]
Wis. Stat. § 100.30 (2003-04).All references to the Wisconsin Statutes hereinafter are to the 2003-04
version unless otherwise noted.

The Wisconsin Unfair Sales Act prohibits Wisconsin
merchants from selling products below cost.The Act also establishes a particular pricing scheme for "motor
vehicle fuel" by defining "cost" for the sale of "motor
vehicle fuel" to include a markup, ranging from 3 percent to 9.18
percent.§ 100.30(2)(am)1m.c.This minimum legal selling price is referred
to as a "minimum markup."Seeinfra n.18-21 and accompanying text.

[3] It is
not disputed that even if motor vehicle fuel does not encompass aviation fuel
within the context of the Unfair Sales Act, aviation fuel cannot be sold below
cost since no vendor can sell any merchandise of any type below cost.Wis. Stat. § 100.30(3).Seealso § 100.30(2)(am)2.
and (c)2.

[4] When
Orion began operating at Wittman on August 21, 2002, its initial price per
gallon on truck-delivered aviation fuel was $2.54.At that time, Basler's truck-delivered aviation fuel price was
$2.59 per gallon.In early September
2002, Orion dropped its truck-delivered aviation fuel to $1.99 per gallon, and
Basler subsequently reduced its price to $1.89 per gallon.Orion then dropped its price to $1.69 per
gallon.On September 28, 2002, Basler
set its price at $1.599 per gallon.Basler
raised its prices in early January 2003 to $1.65 per gallon, on January 8 to
$1.80 per gallon, and again on February 20 to $1.99 per gallon.

Any sale of any item of merchandise either by a
retailer, wholesaler, wholesaler of motor vehicle fuel or refiner, at less than
cost as defined in this section with the intent or effect of inducing the
purchase of other merchandise or of unfairly diverting trade from a competitor,
impairs and prevents fair competition, injures public welfare and is unfair
competition and contrary to public policy and the policy of this section.Such sales are prohibited. Evidence of any
sale of any item of merchandise by any retailer, wholesaler, wholesaler of
motor vehicle fuel or refiner at less than cost as defined in this section
shall be prima facie evidence of intent or effect to induce the purchase of
other merchandise, or to unfairly divert trade from a competitor, or to
otherwise injure a competitor.

Wis. Stat. § 100.30(3).

[6] The
Wisconsin Department of Agriculture, Trade and Consumer Protection
("DATCP") has the statutory authority to "commence an action on
behalf of the state to recover a forfeiture,"
Wis. Stat. § 100.30(4), or "issue a special order as provided
in s. 93.18 against a retailer, wholesaler, wholesaler of motor vehicle fuel or
refiner requiring the person to cease and desist from violating this section in
the sale of cigarettes or other tobacco products, fermented malt beverages,
intoxicating liquor or wine or motor vehicle fuel," § 100.30(5)(a).

[7] Rod
McNeil, Section 100.30, Wisconsin Statutes, The Unfair Sales Act Warning
Letter Complaint number 4139, DATCP, March 21, 2003 (noting that because
Basler's "cost" was $1.78 per gallon, Basler "was no longer in
violation of the Unfair Sales Act" when it "raised its price to $1.80
on January 8, 2003").

Any person who is injured or threatened with
injury as a result of a sale or purchase of motor vehicle fuel in
violation of sub. (3) may bring an action against the person who violated sub.
(3) for temporary or permanent injunctive relief or an action against the
person for 3 times the amount of any monetary loss sustained or an amount equal
to $2,000, whichever is greater, multiplied by each day of continued violation,
together with costs, including accounting fees and reasonable attorney fees,
notwithstanding s. 814.04(1).An action
under this subsection may not be brought after 180 days after the date of a
violation of sub. (3).

Wis. Stat. § 100.30(5m)
(emphasis added).

[10] Rod
McNeil, Retraction in part of warning letter issued March 21, 2003, in File
Number 4139, DATCP, March 21, 2003 (emphasis in original).The court of appeals noted that this
retraction was in response to communications between DATCP and Orion's
attorney.

[12] The
March 19, 2003 Temporary Restraining Order also ordered Basler to produce
"any and all written documentation concerning its purchase and sale of
motor vehicle fuel from September 1, 2002 to the present."

In the case of the retail sale of motor vehicle
fuel by a person other than a refiner or a wholesaler of motor vehicle fuel at
a retail station, the invoice cost of the motor vehicle fuel to the retailer
within 10 days prior to the date of sale, or the replacement cost of the motor
vehicle fuel, whichever is lower, less all trade discounts except customary
discounts for cash, plus any excise, sales or use taxes imposed on the motor
vehicle fuel or on its sale and any cost incurred for transportation and any
other charges not otherwise included in the invoice cost or the replacement
cost of the motor vehicle fuel, plus a markup of 6% of that amount to cover a
proportionate part of the cost of doing business; or the average posted
terminal price at the terminal located closest to the retailer plus a markup of
9.18% of the average posted terminal price to cover a proportionate part of the
cost of doing business; whichever is greater.

In construing rules, ss. 990.001, 990.01,
990.03(1), (2) and (4), 990.04 and 990.06 apply in the same manner in which
they apply to statutes, except that ss. 990.001 and 990.01 do not apply if the
construction would produce a result that is inconsistent with the manifest
intent of the agency.

[19] The
percent markup depends upon whether the vendor is a refiner, a wholesaler, or a
person other than a refiner or wholesaler, whether the vendor sells at a retail
station or at a place other than a retail station, and whether the sale is a
retail sale or wholesale sale.Wis. Stat. § 100.30(2)(am)1m.a.to e.

[29] Wis. Stat. §§ 100.205(1)(c)
("'Rustproofing' means the application of materials and processes intended
or represented to prevent or control rusting or corrosion of a motor vehicle as
defined in s. 340.01(35)"); 100.21(1)(d) (addressing the substantiation of
energy savings or safety claims, "'Motor vehicle' has the meaning provided
under s. 340.01(35)"); 100.42(1)(h) (addressing product safety,
"'Motor vehicle' has the meaning given under s. 340.01(35)");
100.45(1)(c) (addressing mobile air conditioners, "'Motor vehicle' has the
meaning given in s. 340.01 (35)"); and 100.51(5)(1) (addressing motor fuel
dealerships, "'Motor vehicle' has the meaning given in s. 340.01
(35)").

"Motor vehicle" means a vehicle,
including a combination of 2 or more vehicles or an articulated vehicle, which
is self−propelled, except a vehicle operated exclusively on a rail.
"Motor vehicle" includes, without limitation, a commercial motor
vehicle or a vehicle which is propelled by electric power obtained from
overhead trolley wires but not operated on rails. A snowmobile and an
all−terrain vehicle shall only be considered motor vehicles for purposes
made specifically applicable by statute.

"Vehicle" means every device in,
upon, or by which any person or property is or may be transported or drawn upon
a highway, except railroad trains. A snowmobile or electric personal
assistive mobility device shall not be considered a vehicle except for purposes
made specifically applicable by statute.

Wis. Stat. § 340.01(74)
(emphasis added).

[31] In State
v. Welkos, 14 Wis. 2d 186, 192, 109 N.W.2d 889 (1961), this court
reasoned that because the legislature had amended one statute but did not make
a like change to a similar statute, the omission of that new provision from the
similar statute demonstrated a different intent.

To make and enforce such regulations, not
inconsistent with law, as it may deem necessary for the exercise and discharge
of all the powers and duties of the department, and to adopt such measures and
make such regulations as are necessary and proper for the enforcement by the
state of chs. 93 to 100, which regulations shall have the force of law.

Wis. Stat. § 93.07(1).

[33] Orion
also asserts that the legislature ratified DATCP's definition when it amended
the Unfair Sales Act.Because we find
the code ambiguous, we do not reach this issue.

[34] Under
this statute, "the exclusive means of judicial review of the validity of a
rule shall be an action for declaratory judgment as to the validity of such
rule brought in the circuit court for Dane County."Wis. Stat. § 227.40.

[35] Wis. Stat. § 227.15(1)
("Prior to a public hearing on a proposed
rule . . . an agency shall submit the proposed rule to the
legislative council staff for review . . . .").This statute has not changed and was in
effect in 1989.

[37] Wis. Stat. § 227.19(2)
("An agency shall submit a notice to the presiding officer of each house
of the legislature when a proposed rule is in final draft form.").This statute has not changed and was in
effect in 1989.

[44] Rod
McNeil, Retraction in part of warning letter issued March 21, 2003 in File
Number 4139, DATCP, March 21, 2003.Basler asserts in its briefs and oral argument that this retraction was
in response to communications between DATCP and Orion's attorney.Orion does not dispute this.

[46] We
note that the United States Supreme Court recently concluded that an agency's
interpretation of an unambiguous regulation contained in an opinion
letter, as opposed to interpretations that result from the adversarial process
or an agency's explicit rule-making authority, "lack[s] the force of law
[and therefore] do[es] not warrant Chevron-style deference."Christensen v. Harris County, 529
U.S. 576, 587 (2000) (examining the agency's interpretation of its unambiguous
regulation) (citations omitted).In Chevron,
the United States Supreme Court concluded that when an agency's regulation
represents a reasonable interpretation of the statute and does not conflict
with the statute, the rule is entitled to deference.Chevron U.S.A., Inc. v. Natural Resources Defense Council,
Inc., 467 U.S. 837, 842-44 (1984).

The Court also determined that even if an opinion
letter is not entitled to deference, the letter is entitled to
"respect" to the extent that the interpretation is persuasive.Christensen, 529 U.S. at 587 (citing Skidmore
v. Swift & Co., 323 U.S. 134, 140 (1944)).

Yet, the Court continued, "an agency's
interpretation of its own regulation is entitled to
deference . . . when the language of the regulation is ambiguous."Christensen, 529 U.S. at 588
(emphasis added) (citing Auer v. Robbins, 519 U.S. 452, 461
(1997) (concluding that an agency interpretation of its own ambiguous
regulation is controlling unless the interpretation is plainly erroneous or
inconsistent with the regulation)).The
United States Supreme Court did not address, however, the degree of deference
due to an agency's interpretation of its ambiguous regulation in either Auer
or Christensen.

Relying on Christensen, a Wisconsin federal
court similarly concluded that because the regulation in question was
ambiguous, the informal interpretation of that regulation by the agency that
promulgated the regulation was entitled to some level of deference.DeBraska v. City of Milwaukee, 131 F.
Supp. 2d 1032, 1034-35 (E.D. Wis. 2000) (examining the preamble to the
regulations under review, a 1994 opinion letter by an administrator in the
Department, and an amicus curiae brief filed on behalf of one of the parties in
the case) (citing Auer, 519 U.S. at 461).

We note that neither party briefed or argued this
issue, and we decline to reach it.

[48] The
Act prohibited any retailer or wholesaler from advertising, offering for sale,
or selling any merchandise below "cost."Wisconsin's Unfair Sales Act: An Overview,
Staff Brief 80-10, Wisconsin Legislative Council Staff, July 9, 1980 (emphasis
added)."Cost" included a
minimum markup of 3 percent for wholesalers and 6 percent for retailers for all
merchandise.Id.This court concluded that the minimum markup
scheme was constitutional.Ross,
259 Wis. 379.

[56] Revisions
in the State Minimum Markup Law (1985 Wisconsin Act 313), Information
Memorandum 86-12, Wisconsin Legislative Council Staff, May 9, 1986.The 1986 revision also made violations of
the Act subject to civil forfeitures, rather than criminal penalties, and
granted DATCP the authority to independently enforce the statute by bringing a
claim in court or issuing a cease and desist order.

[58] The
same references to the definition of "motor vehicle" in
Wis. Stat. § 340.01(35) in Chapter 100 exist under the current
statutes.See
Wis. Stat. §§ 100.205(1)(c); 100.21(1)(d); 100.42(1)(h)
(2003-04).

[60] Wis. Stat. § 340.01(74)
(1983-84) (emphasis added). The definitions of "motor vehicle" and
"vehicle" are substantially the same today as they were when the
Unfair Sales Act was amended in 1986.See,
supra, ¶24.